Mitigating the Impact of Dietary Lipid Peroxidation on Rainbow Trout Fry ( Oncorhynchus mykiss ): The Stabilizing Role of Grape Seed Extract on Intestinal Integrity and Metabolic Homeostasis

ABSTRACT

In this study, we investigated whether dietary grape seed extract (GSE) mitigates the effects of oxidized fish oil on intestinal structural indices, serum biochemical responses, and growth performance in rainbow trout ( Oncorhynchus mykiss ). Fish were fed six diets for 30 days: fresh fish oil without GSE (GSE0), with 0.1% GSE (GSE1), or with 0.3% GSE (GSE3), and oxidized fish oil without GSE (OX‐GSE0), with 0.1% GSE (OX‐GSE1), or with 0.3% GSE (OX‐GSE3). Morphometric and histomorphometric analyses showed treatment‐dependent alterations in the structural indices of the intestine and pyloric ceca. The most unfavorable histomorphometric response was observed in OX‐GSE3, whereas OX‐GSE1 and GSE1 showed more favorable fold height, enterocyte height, and tunica muscularis thickness ( p  < 0.05). Serum biochemical profiles indicated an oxidation‐dependent response to GSE, with changes in glucose, cholesterol, and triglycerides suggesting partial modulation of metabolic stress ( p  < 0.05). Growth performance and feed utilization were characterized primarily by significant Oil × GSE interactions, indicating that GSE responses depended on the oxidation status of dietary oil. OX‐GSE1 improved growth‐related responses compared with OX‐GSE0, whereas OX‐GSE3 provided no additional benefit. Overall, 0.1% GSE mitigated selected adverse effects of oxidized fish oil in an oxidation‐dependent manner, suggesting its potential as a dietary strategy against lipid peroxidation‐related stress.

Practical Applications : The study provides a dose‐selection framework for researchers and feed formulators using grape seed extract, a winery by‐product, when aquafeed lipids are susceptible to oxidation. The response was dose‐dependent: 0.1% GSE supported intestinal structural indices and growth‐related outcomes under oxidized‐oil conditions, whereas 0.3% did not yield additional benefit. Accordingly, antioxidant inclusion rates should be selected alongside measures of oil quality rather than on the assumption that higher extract levels are more effective. This approach may support both the management of peroxidized lipids in fish feeds and the value‐added use of grape‐processing residues. Longer commercial‐scale trials are needed before routine application.